// © 2016 and later: Unicode, Inc. and others.
// License & terms of use: http://www.unicode.org/copyright.html
/*
 *******************************************************************************
 * Copyright (C) 1996-2005, International Business Machines Corporation and    *
 * others. All Rights Reserved.                                                *
 *******************************************************************************
 */
package com.ibm.icu.text;

import java.text.ParsePosition;

/**
 * An interface that defines both lookup protocol and parsing of symbolic names.
 *
 * <p>This interface is used by UnicodeSet to resolve $Variable style references that appear in set
 * patterns. RBBI and Transliteration both independently implement this interface.
 *
 * <p>A symbol table maintains two kinds of mappings. The first is between symbolic names and their
 * values. For example, if the variable with the name "start" is set to the value "alpha" (perhaps,
 * though not necessarily, through an expression such as "$start=alpha"), then the call
 * lookup("start") will return the char[] array ['a', 'l', 'p', 'h', 'a'].
 *
 * <p>The second kind of mapping is between character values and UnicodeMatcher objects. This is
 * used by RuleBasedTransliterator, which uses characters in the private use area to represent
 * objects such as UnicodeSets. If U+E015 is mapped to the UnicodeSet [a-z], then
 * lookupMatcher(0xE015) will return the UnicodeSet [a-z].
 *
 * <p>Finally, a symbol table defines parsing behavior for symbolic names. All symbolic names start
 * with the SYMBOL_REF character. When a parser encounters this character, it calls parseReference()
 * with the position immediately following the SYMBOL_REF. The symbol table parses the name, if
 * there is one, and returns it.
 *
 * @stable ICU 2.8
 */
public interface SymbolTable {

    /**
     * The character preceding a symbol reference name.
     *
     * @stable ICU 2.8
     */
    static final char SYMBOL_REF = '$';

    /**
     * Lookup the characters associated with this string and return it. Return {@code null} if no
     * such name exists. The resultant array may have length zero.
     *
     * @param s the symbolic name to lookup
     * @return a char array containing the name's value, or null if there is no mapping for s.
     * @stable ICU 2.8
     */
    char[] lookup(String s);

    /**
     * Lookup the UnicodeMatcher associated with the given character, and return it. Return {@code
     * null} if not found.
     *
     * @param ch a 32-bit code point from 0 to 0x10FFFF inclusive.
     * @return the UnicodeMatcher object represented by the given character, or null if there is no
     *     mapping for ch.
     * @stable ICU 2.8
     */
    UnicodeMatcher lookupMatcher(int ch);

    /**
     * Parse a symbol reference name from the given string, starting at the given position. If no
     * valid symbol reference name is found, return null and leave pos unchanged. That is, if the
     * character at pos cannot start a name, or if pos is at or after text.length(), then return
     * null. This indicates an isolated SYMBOL_REF character.
     *
     * @param text the text to parse for the name
     * @param pos on entry, the index of the first character to parse. This is the character
     *     following the SYMBOL_REF character. On exit, the index after the last parsed character.
     *     If the parse failed, pos is unchanged on exit.
     * @param limit the index after the last character to be parsed.
     * @return the parsed name, or null if there is no valid symbolic name at the given position.
     * @stable ICU 2.8
     */
    String parseReference(String text, ParsePosition pos, int limit);
}
